Firing circuit and method of operating the circuit

• US 6,225,707 B1
• Filed: 06/09/2000
• Issued: 05/01/2001
• Est. Priority Date: 12/09/1997
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Hermann, Stefan
• Primary Examiner(s): Ballato, Josie
• Assistant Examiner(s): DeBeradinis, Robert L
• Application Number:
  US09/591,302
• Time in Patent Office: 326 Days
• Field of Search: 307/10.1, 280/735, 180/274
• US Class Current: 307/10.1
• CPC Class Codes: B60R 21/017 including arrangements for providing electric power to safety arrangements or their actuating means, e.g. to pyrotechnic fuses or electro-mechanic valves
• CPC Class Codes: F42D 1/05 Electric circuits for blasting

Abstract

In order to minimize the overall size of a firing capacitor and to minimize the energy which is not utilized during a firing operation, the firing capacitor charge voltage U₀ is set to be equal to 2*R*I, where R designates the internal resistance of the firing cap and I designates the firing current. The capacitance value C₀ of the firing capacitor is set to C₀=T/R, where T designates the period for which the firing current flows.

Claims

1. A method of operating a firing circuit configured to actuate a firing cap of a firing system, the firing circuit including a firing capacitor for storing energy necessary to fire the firing cap, and a switch connected between the firing capacitor and the firing cap, and wherein the firing cap has a given internal resistance and is fired with a current having a value at least as high as a predefined minimum current value and a duration of at least a given minimum time period, the method comprising the following steps:

charging the firing capacitor to a charge voltage of 2.0 to 2.4 times a product of the internal resistance of the firing cap and the current supplied to the firing cap during a firing operation;

limiting the current, during the firing operation, to a value corresponding to 1.0 to 1.2 times the minimum current value; and

setting a capacitance of the firing capacitor to a capacitance value corresponding to 1.0 to 1.2 times the given minimum time period divided by the internal resistance of the firing cap.

2. The method according to claim 1, which comprises operating the firing circuit as an integral member of a vehicle occupant protection system of a motor vehicle.

3. A firing circuit for firing a firing cap having a predefined internal resistance and, for firing, requiring a supply of current having a value at least equal to a predefined minimum current value and a duration of at least a predefined minimum time period, the firing circuit comprising:

at least one firing capacitor;

p1 a voltage or current source connected to and charging said firing capacitor to a specific charge voltage;

a switch for connecting said firing capacitor to the firing cap during a firing operation; and

a current limiter limiting a current flowing to the firing cap during the firing operation to 1.0 to 1.2 times a minimum current value specified for the firing cap;

said firing capacitor having a charge voltage set to 2.0 to 2.4 times a product of the limited current flowing to the firing cap and an internal resistance of the firing cap; and

said firing capacitor having a capacitance set to 1.0 to 1.2 times the minimum time period divided by the internal resistance of the firing cap.

4. The firing circuit according to claim 3, wherein the current limiter is integrated into said switch.

5. In combination with a motor vehicle occupant protection system, the firing circuit according to claim 3.

6. The combination according to claim 5, wherein the firing cap is a squib of an airbag system and the firing circuit is a trigger circuit for the airbag system.